17 research outputs found
Unitarity and On-Shell Recursion Methods for Scattering Amplitudes
This thesis describes some of the recent (and some less recent) developments in calculational techniques for scattering amplitudes in quantum field theory. The focus is on on-shell recursion relations in complex momenta and on the use of unitarity methods for loop calculations. In particular, on-shell recursion is related to the MHV rules for computing tree-level gauge amplitudes and used to extend the MHV rules to graviton scattering. Combinations of unitarity cut techniques and recursion are used to argue for the "No-Triangle Hypothesis" in N=8 supergravity which is related to its UV behaviour. Finally, combinations of unitarity and recursion are used to demonstrate the full calculation of a one-loop amplitude involving a Higgs particle and four gluons in the limit of large top mass. The present version is edited to incorporate some of the comments and suggestions of the evaluation committee, but has not been updated for developments in the meantime
A direct proof of the CSW rules
Using recursion methods similar to those of Britto, Cachazo, Feng and Witten
(BCFW) a direct proof of the CSW rules for computing tree-level gluon
amplitudes is given.Comment: 11 pages, uses axodraw.st
The No-Triangle Hypothesis for N=8 Supergravity
We study the perturbative expansion of N=8 supergravity in four dimensions
from the viewpoint of the ``no-triangle'' hypothesis, which states that
one-loop graviton amplitudes in N=8 supergravity only contain scalar box
integral functions. Our computations constitute a direct proof at six-points
and support the no-triangle conjecture for seven-point amplitudes and beyond.Comment: 43page
MHV-Vertices for Gravity Amplitudes
We obtain a CSW-style formalism for calculating graviton scattering
amplitudes and prove its validity through the use of a special type of
BCFW-like parameter shift. The procedure is illustrated with explicit examples.Comment: 21 pages, minor typos corrected, proof added in section
One-Loop NMHV Amplitudes involving Gluinos and Scalars in N=4 Gauge Theory
We use Supersymmetric Ward Identities and quadruple cuts to generate n-pt
NMHV amplitudes involving gluinos and adjoint scalars from purely gluonic
amplitudes. We present a set of factors that can be used to generate one-loop
NMHV amplitudes involving gluinos or adjoint scalars in N=4 Super Yang-Mills
from the corresponding purely gluonic amplitude.Comment: 16 pages, JHEP versio
Higgs amplitudes from twistor inspired methods
We illustrate the use of new on-shell methods, 4-dimensional unitarity cuts
combined with on-shell recursions relations, by computing the
A_4^{(1)}(phi,1^-,2^-,3^+,4^+) amplitude in the large top mass limit where the
Higgs boson couples to gluons through an effective interaction.Comment: 4 pages, two figures, based on talks given at the Cracow Epiphany
Conference on Precision Physics and Monte Carlos for LHC 4 - 6 January 2007,
Cracow, Poland and the 42nd Rencontres de Moriond QCD and High Energy
Hadronic Interactions, March 17-24, La Thuile, Ital
One-loop phi-MHV amplitudes using the unitarity bootstrap
We consider a Higgs boson coupled to gluons via the five-dimensional
effective operator H Tr G_{munu}G^{munu} produced by considering the heavy top
quark limit of the one-loop coupling of Higgs and gluons in the standard model.
We treat H as the real part of a complex field phi that couples to the selfdual
gluon field strengths and compute the one-loop corrections to amplitudes
involving phi, two colour adjacent negative helicity gluons and an arbitrary
number of positive helicity gluons - the so-called phi-MHV amplitudes. We use
four-dimensional unitarity to construct the cut-containing contributions and
the recently developed recursion relations to obtain the rational contribution
for an arbitrary number of external gluons. We solve the recursion relations
and give explicit results for up to four external gluons. These amplitudes are
relevant for Higgs plus jet production via gluon fusion in the limit where the
top quark mass is large compared to all other scales in the problem.Comment: 40 pages, 11 eps figures, JHEP3 class, references adde